1. Field of the Invention
The present invention relates to a manual combinatorial weighting apparatus for manually placing batches of articles to be weighed on a plurality of scale plates and selecting a combination of article batches which exhibits a weight that is the same as or closest to a desired weight.
2. Description of the Prior Art
Large-scale supermarkets have packaging plants where articles or commodities are packaged. In some cases, a number of fish or fish or meat slices are packaged in a prescribed weight range.
Normally, fish slices or meat cuts are delivered on a belt converyor, and a plurality of weighing units including scale plates are disposed on a rack disposed on one side of the belt conveyor or on racks disposed on opposite sides of the belt conveyor. The fish slices or meat cuts are weighed as batches of artiches on the scale plates. The detected weight values of the batches of articles are combined in a number of ways, and a combination of article batches which has a weight value which is the same as or closest to a desired weight is selected. The scale plates carrying the selected combination of article batches are indicated, and the article batches are removed from those scale plates. There is known in the art a manual combinatorial weighing apparatus including a control unit which can carry out the above combinatorial weighing procedure, as disclosed in Japanese Utility Model Publication No. 61-35932 and Japanese Laid-Open Utility Model No. 56-170728.
In the above manual combinatorial weighing apparatus, five to ten, or more, scale plates and weighing units are mounted on a narrow elongate rack or racks, and the belt conveyor for feeding the articles is attached to the rack or racks. Therefore, the manual combinatorial weighing apparatus is elongate and large in size. This is disadvantageous in that the freedom to install the manual combinatorial weighing apparatus in a plant is small, and there are large limitations on the installation of the manual combinatorial weighing apparatus. Each of the weighing units must be kept horizontal, resulting in a complex adjustment process.
When weighing units are selected as giving a combination of article batches exhibiting a desired weight, indicator lamps are energized. The indicator lamps are de-energized when the articles are taken away from the scale plates. The timing of de-energizing the indicator lamps is critical. If the indicator lamps were de-energized before the articles are completely removed from the scale plates, e.g., if the indicator lamps were turned off immediately after the articles are grabbed by the operator, the operator would tend to place articles again on the scale plates in error. Some conventional manual combinatorial weighing apparatus have failed to fully control the indicator lamps.
In certain manual combinatorial weighing apparatus, when a batch combination giving a desired weight is found, a command signal is applied to the indicator lamps of those weighing units which are selected as providing such a batch combination to hold the indicator lamps energized for a certain period of time. The indicator lamps are de-energized only when all of the articles are completely removed from the selected scale plates so that the displyed weights are cleared to zero or a negative value. If a small amount of sticky food materials such as daily dishes or soft cheese, for example remains on a scale plate, the indicator lamp therefor is not de-energized, and a next weighing cycle cannot be initiated. Articles or commodities to be weighed by manual combinatorial weighing apparatus vary in shape, stickiness, and other properties. For weighing soft elongate articles, such as fish, it is customary for the operator to manually hold the articles, place part of the articles on the scale plate, move them slowly toward the center of the scale plate, and finally release them. Where an article to be weighed is sticky, it takes a considerable time before the sticky article falling by gravity from article feeders on to scale plates is fully distributed and put on the scale plates. In this case, the manual combinatorial weighing apparatus effects combinatorial weighing operation several times while the article is not yet put to prescribed quantities on the scale plates. Therefore, as shown in FIG., 1 of the accompanying drawings, the weight data produced by the weight units tend to vary; they first reach a temporary stable weight value X, and then increase until they reach a true stable weight value Y. If the process for finding a suitable weight combination were effected at the stable point X, then a proper weight combination could not be selected, but an erroneous weight might be selected.
Another problem with the combination combinatorial weighing apparatus is that when the apparatus is in use for a long period of time, the zero point may be shifted due to a temperature-dependent drift or a dust deposit. If the zero point is shifted in a direction to increase the detected weights, those weighing units which do not carry any articles take part in a combinatorial weighing process. When this happens, packages with incorrect weights are produced, and the indicator lamps associated with empty scale plates that are selected remain energized. Where the manual combinatorial weighing apparatus has a target weight of 500 g, an upper limit weight of 504 g, and a lower limit weight of 498 g, if no proper weight combination is obtained and weighing units A, B, C are selected as giving a combination weight of 516 g stored in a processing unit, an error or deviation displayed is (516-500)=16 g, and the operator must replace the articles on the weighing units so that the displayed error will fall within a range of from -2 g to+4 g. It would be quite difficult for the error to fall in that range by replacing the articles only once, and the operator must usually replace the articles several times. Therefore, the efficiency is poor.